Modeling the depleting mechanism of urea‐water‐solution droplet for automotive selective catalytic reduction systems

Abstract

in Wiley Online Library (wileyonlinelibrary.com).The current work aims to develop a reliable theoretical model capable of simulating the depletion process of urea-water-solution (UWS) droplets injected in a hot exhaust stream as experienced in an automotive urea-based selective catalytic reduction system. A modified multicomponent vaporization model is presented and implemented in the current study to simulate the behavior of UWS droplet in heated environment. Although water depletion is modeled as a vaporization process, urea depletion is modeled using two different approaches: (i) vaporization and (ii) direct thermal decomposition. The suitability of both depletion approaches is assessed in the current study by comparison with experimental data of the decay of a single UWS droplet in a quiescent heated environment. The decay rate of UWS droplet is accurately predicted with the multicomponent vaporization model. The possibility of internal gasification is demonstrated. Based on the complex decomposition behavior of urea, the current study proposes a decomposition mechanism for UWS droplet. The suitability of implementing the rapid mixing approach is assessed through comparison with the diffusion limit approach at various operating conditions and initial UWS droplet sizes. V V C 2011 American Institute of Chemical Engineers AIChE J, 57: 3210-3225, 2011

Urea-Water Droplet Phase Change and Reaction Modelling: Multi-Component Evaporation Approach

“…The study of Birkhold et al (2007) shows that a rapid mixing model is sufficient and computationally cheap for urea injection studies with no significant improvement using the diffusion limit model. Abu-Ramadan et al (2011) report that the deviation between the rapid mixing and the diffusion limit models is significant only at lower temperatures and for large droplet sizes. Ryddner and Trujillo (2015) suggest that in case of water entrapment inside the shell of precipitated urea, the diffusion limit model is more appropriate to capture the spatial variation in the concentration of urea inside a droplet.…”

“…In this approach the initiation of urea evaporation occurs before the complete depletion of water content. ClasiusClayperon equation and the experimental data of Emel 'Yanenko et al (2006) are used by Abu-Ramadan et al (2011) to analytically calculate the saturation vapor pressure. The first law of thermodynamics is used to derive the urea latent heat of vaporization variation with temperature, required in the calculation of saturation pressure.…”

“…Alternative to direct thermolysis is multi-component vaporization approach. Abu-Ramadan et al (2011) conducted studies on a single droplet of urea-water solution, using direct thermolysis and multicomponent vaporization approaches. The comparison shows better suitability of vaporization approach over direct thermolysis in terms of droplet depletion rates and droplet temperatures.…”

Concept of Vaporized Urea Dosing in Selective Catalytic Reduction

“…The exact state of aggregation of urea during decomposition is still uncertain [15,16]. Two recent theoretical studies [17,18] …”

Investigation on UWS evaporation for vehicle SCR applications

“…He established a quickly hybrid model. Abu-Ramadan et al 18 believes that there is a gradient of concentration and temperature inside the droplets. Munnannur and Liu, 19 Ebrahimian and Habchi 20 simulated the evaporation process in detail by the using of a multicomponent evaporation model.…”